1. Field of the Invention.
This invention relates to interferometric systems, materials and techniques that can used to examine one or more cells.
2. Description of Related Art.
Cells are capable of many complex functions such as motility, cell-cell communication and the synthesis of a wide variety of biologically active molecules. Cell membranes play a crucial role in many of these functions in part due to their ability to adopt a wide variety of morphological configurations, configurations which depend on factors such as cellular physiology as well as cell type and lineage specific functions.
Cell membranes and other physical structures of cells are complex and dynamic, with cytoskeletal elements oriented in many directions, and thus their mechanical properties are highly anisotropic, and vary widely among individual cells within a population (see, e.g. Smith et al., (2003) American Journal of Physiology-Lung Cellular and Molecular Physiology 285, L456-L463; Hu et al., (2003) American Journal of Physiology-Cell Physiology 285, C1082-C1090; Fabry et al., (2001) Physical Review Letters 8714; and Fabry et al., (2001) Journal of Applied Physiology 91, 986-994). The degree and significance of this mechanical anisotropy and its population variances is poorly characterized, however, due to methodological limitations of existing nano-mechanical probing techniques.
Existing cytometric approaches, such as those using AFM (see, e.g. Mahaffy et al., (2004) Biophysical Journal 86, 1777-1793), and high-magnification particle tracking microrheology (see, e.g. Weihs et al., (2006) Biophysical Journal 91, 4296-4305), are simply too slow to adequately measure the number of individual cells required for population comparisons. On the other hand, wide-field magnetic/optical bead tracking methods, which rely on beads fixed to the cell surface, can only track the probe with sufficient accuracy (tens of nanometers (see, e.g. Mijailovich et al., (2002) Journal of Applied Physiology 93, 1429-1436; and Cheezum et al., (2001) Biophysical Journal 81, 2378-2388) in two dimensions (the x-y plane perpendicular to the objective).
In view of the limitations with existing cytometric technologies, there is a specific need to extend probe-based mechanical measurements into all three dimensions, while retaining measurement accuracy and high throughput. In addition, there is a general need in the art for optimized methods of observing and/or determining one or more characteristics of a cell (e.g., determining the physiological status or biological state of a cell; determining the cell type of a cell; determining the response of a cell to a biochemical event; etc.). The instant invention addresses these needs.